Effects Of Clorgyline Research Articles

Effect of clorgyline (a MAO type A inhibitor) on locomotor activity in the Syrian hamster.

Syrian hamsters in a lighting schedule of 14 h of light per day (LD 14:10) and housed in cages equipped with running wheels exhibited a clear onset of locomotor activity during the 1st h after lights off. Implantation of osmotic minipumps containing clorgyline (2 mg . kg-1 . day-1), an irreversible inhibitor of monoamine oxidase type A, caused a 1.5-h delay in the onset of wheel running by the 7th day of treatment. Increasing dosages of clorgyline (0.5, 1, 2, or 4 mg . kg-1 . day-1) caused increasing delays. Hamsters shifted from LD 14:10 to LD 10:14 underwent a 3-h advance in the onset of wheel running. Animals treated with clorgyline (2 mg . kg-1 . day-1) exhibited a markedly slowed rate of advance in activity onset, which did not prevent the short photoperiod from inhibiting reproductive function. Additionally, removal of the pineal gland did not affect wheel-running onset and did not prevent the delay in activity onset during clorgyline treatment. Hamsters in LD 14:10 were "released" into constant darkness (DD) for 3 days to prevent masking of activity onsets and offsets by light. Delays in activity onset in LD 14:10 caused by clorgyline (2 mg . kg-1 . day-1) persisted when these animals were released into DD. Activity offset in LD 14:10 occurred at lights on before and during clorgyline treatment but was delayed when the treated animals were maintained in DD. Drug-induced delays in both activity onset and offset suggest that clorgyline is not simply shortening the duration of activity or changing the expression of activity relative to the light-dark cycle, but is delaying the phase position of the circadian rhythm in locomotor activity. Clorgyline may act directly on the central oscillatory mechanism that drives the rhythm.

Regional inhibition of monoamine oxidase activity by administration of clorgyline in rat brain.

The inhibiting effect of monoamine oxidase (MAO) activities towards 5-hydroxytryptamine, dopamine and beta-phenylethylamine by an acute and chronic administration of clorgyline was investigated in five locations of the rat brain. Inhibiting the percentage distributed unevenly in each hypothalamic nucleus and in the circumventricular areas, except the median eminence, the percentages were significantly low as compared with the hypothalamic lateral nucleus. A significant percentage of inhibition for type B MAO towards beta-phenylethylamine was noticed in the chronically administered group. In conclusion, the MAO-inhibiting effect of clorgyline administered intraperitoneally was unevenly distributed in the discrete brain nuclei and the regional difference depended upon the dose and the duration of the clorgyline administration.

Effects of clorgyline and deprenil on corticosterone levels in rats

Adrenal and plasma corticosterone levels were measured in adult female rats after i.p. administration of specific MAO inhibitors: clorgyline (IMAO-A) and deprenil (IMAO-B). Brain and adrenal MAO activity was also determined. The IMAO effect was found to depend on 3 interrelated factors: (a) dose of drug, (b) time after injection, (c) specificity in MAO inhibition. One hour after injection, clorgyline (1 and 2.5 mg/kg) but not deprenil (20 mg/kg), appeared to inhibit the adrenocortical stress response to i.p. injection. At higher doses, MAO-B inhibition by deprenil (40 mg/kg) induced a moderate but sustained increase in corticosterone levels, while MAO-A inhibition by clorgyline (5, 10, 20 mg/kg) resulted in a large and sharp rise. This effect of clorgyline was potentiated with α-methyl-p-tyrosine and blocked with p-chlorophenylalanine. On this basis, the involvement of serotonergic mechanisms could be considered to explain the stimulatory effect of clorgyline on adrenal cortical function.

Lifetime monoamine oxidase inhibition and sleep

The effects of clorgyline, a type A monoamine oxidase (MAO) inhibitor, on the sleep of the rat were examined after subacute and lifetime administration. When 2 mg/kg/24 hours were given for 60 hours, type A MAO was inhibited by 92% and a significant reduction in REM sleep time was noted. When fetal rats were exposed to maternal dosage of 1 mg/kg/24 hours and then received this dose from one to 6 weeks postnatally, type A MAO was inhibited by 99%, but there were no alterations in the EEG sleep stages. In summary, subacute administration of clorgyline resulted in decreases in both Type A MAO and REM sleep; during chronic administration in a developing animal, Type A MAO was again decreased, but there was no corresponding changes in REM sleep.

Effects of selective inhibition of type A and type B monoamine oxidase on intraocular pressure in the cat and the rabbit.

Ocular tension of conscious cats and rabbits was measured after topical application of clorgyline, a selective inhibitor of type A monoamine oxidase, or deprenyl, a selective inhibitor of line (1,4 and 12%) showed a dose-related reduction of intraocular pressure, with maximal lowerings amounting to 6 to 7 mm Hg. Pretreatment of eyes with clorgyline, 1%, markedly potentiated the pressure lowering response to epinephrine, 0.1%, applied topically. Sympathetic denervation almost completely abolished the effect of clorgyline. In contrast, deprenyl (2 to 8%) did not lower intraocular pressure after topical application to cat or rabbit eyes. beta-Phenylethylamine (2 to 16%) a specific substrate for the B form of monoamine oxidase, likewise did not lower ocular tension when given either alone or after pretreatment with deprenyl. These findings suggest that the intraocular pressure lowering effect of monoamine oxidase inhibitors is due primarily to inhibition of the A form of the enzyme and is dependent on intact sympathetic innervation.

Antagonism between long acting Monoamine Oxidase Inhibitors (MAOI) and MD780515, a new specific and reversible MAOI

The inhibition of type A and B monoamine oxidase (MAO A and B) in rat brain, liver and heart by MD780515, 3-[4-(3 cyanophenylmethoxy) phenyl]-5-(methoxymethyl)-2-oxazolidinone, has been investigated ex vivo with 5-hydroxytryptamine (5-HT) and β-phenylethylamine (PEA) as substrates. MAO A was strongly inhibited for four hours after oral administration of 10 mg/kg MD780515 (maximum inhibition : 72%, 86% and 83% in brain, liver and heart respectively. In contrast, in heart where PEA is deaminated by type A MAO, the predominant form of MAO in that tissue, the inhibition was 68% 30 minutes after administration of the compound. In all cases, MAO activities reached control values 24 hours after drug administration (10 mg/kg), whereas some inhibitory activity was still present 24 hours after oral administration of higher doses. The strong MAO A inhibition (68 to 83%) remaining in the three tissues 24 hours after oral administration of clorgyline (5 mg/kg) was completely removed by pretreatment with MD780515 (10 mg/kg). In the same conditions, MD780515 protected against the inhibition (53%) by clorgyline of PEA deamination in heart. Oral pretreatment with increasing doses of MD780515 (2.6 to 84 mg/kg) gradually removed brain MAO A inhibition caused by clorgyline (92%, 28.2 mg/kg) or tranylcypromine (88%, 4.8 mg/kg), the complete removal being observed at the dose of 21 mg/kg of MD780515 for clorgyline, and at 42 mg/kg for tranylcypromine. Inhibition of brain MAO B by tranylcypromine (96%) was not modified by pretreatment with the same range of oral doses of MD780515. The results are consistent with a specific and reversible inhibition of MAO A activity by MD780515 which can protect against long acting MAO A inhibitory effects of clorgyline and tranylcypromine. MD780515 enhances the selectivity of tranylcypromine.

Biochemical characterization of the active site of brain monoamine oxidase.

Until recently little was known concerning the chemical details of the mechanism of interaction of flavin-linked mitochondrial membrane bound monoamine oxidase (MAO) with its substrates and inhibitors. Substrates which have enzymes as their targets have been valuable in elucidating active site residues and structural features. Acetylenic amines as exemplified by clorgyline, deprenyl and pargyline are called 'suicide inhibitors' because an irreversible inhibitor is formed by the action of MAO from a relatively innocuous compound which acts as a substrate. These inhibitors can selectively inactivate MAO 'type A' and/or 'type B'. MAO isolated in homogeneous form from liver or kidney contains 1 mole of covalently bound coenzyme, cysteinyl-flavin, per mole enzyme. The flavin is bound to a pentapeptide via the thio-ether of cysteine at the 8 alpha-position of the isoalloxazine. A comparison of the inhibitory effects of clorgyline, deprenyl and pargyline on liver enzyme preparations from bovine or rat have confirmed our expectation that these irreversible inactivators form the same type of adduct with the cysteinyl-flavin active site of MAO 'type A' and 'type B', and that binding is stoichiometric at the N-5 of the covalently bound flavin in a flavocyanine linkage. Substrates protect from inhibition. In contrast to the reported observation of Tipton (39), pig brain mitochondrial MAO purified by two alternative methods contains cysteinyl-flavin in substantial amounts. The turnover number of enzyme from brain per mole of cysterinyl-flavin in apparently homogeneous samples is nearly the same as that of highly purified kidney and liver enzyme. Thus it is apparent that brain MAO also contains cysteinyl-flavin at the active center and therefore it is expected that acetylenic as well as hydrazine inhibitors form the same linkage with the flavin moiety as that formed with enzyme from peripheral tissues. A specific inhibitor for the deamination and potentiation of dopamine formed in the brain of Parkinsonian patients after treatment with L-Dopa has been regarded desirable. Deprenyl, a selective MAO 'type B inhibitor without the 'cheese effect', is the most potent inactivator of human brain MAO, and clinical results show that the drug is very useful in the treatment of Parkinson's disease and depression.

Developmental aspects of rat heart monoamine oxidase

Rat heart mitochondria were demonstrated to contain two forms of monoamine oxidase which resemble the A and B forms found in other tissues on the basis of the effects of clorgyline, thermostability, and kinetic characteristics. The relative amounts of these two enzyme forms underwent a marked change between 3 and 15 weeks of age. In the adult, only the form resembling type A MAO could be demonstrated.

Cumulative effects of irreversible MAO inhibitors in vivo

The effects of repeated treatment with clorgyline, pargyline, deprenyl and tranylcypromine on MAO activity in rat brain and liver were investigated. MAO was measured with the substrates serotonin (5HT), phenethylamine (PEA) and, in some cases, t brain tissue after single and repeated administrations of 10 mg/kg s.c. clorgyline or deprenyl were also compared. Single doses of clorgyline (1 and 10 mg/kg s.c.) completely blocked the deamination of 5-HT. PEA deamination gradually decreased during the 14-day treatment. Pargyline in a dose of 0.3 mg/kg s.c. reduced both 5-HT and PEA deamination progressively over the same period. In the course of repeated treatment the effects of clorgyline and deprenyl on 5-HT and PEA deamination increased in intensity, by a factor of about 10 in the brain and about 3 in the liver. The potentiation of the effect of tranylcypromine was less marked (brain: × 4; liver: × 2). The rates of recovery of MAO activity were not greater after repeated than after single administrations of high doses of clorgyline and deprenyl, suggesting that the withdrawal of the drugs is not followed by a rebound phenomenon. Our results indicate that repeated treatment with suitable doses of clorgyline or deprenyl leads to specific reduction of either MAO A or B activity in brain, without producing any appreciable effect in the liver.

NONEXISTENCE OF A TYPE C MONOAMINE OXIDASE IN RAT BRAIN

Abstract— The possible existence of type C MAO, distinct from type A and type B, in circumventricular structures of rat brain was examined by histological studies on the inhibitory effects of clorgyline. a preferential type A MAO inhibitor and deprenyl, a preferential type B inhibitor, on enzyme. Brain slices were preincubated with the inhibitors and then incubated with 5‐HT, the substrate for type A MAO, and stained for MAO activity. Deposits of the product formazan were detected in circumventricular structures of slices of brain preincubated with clorgyline and deprenyl at concentrations of 10‐7–10‐4m at room temperature for 5 min. When the slices were preincubated with either of these inhibitors at room temperature for 60 min, strong activity was observed in this region, whereas when they were preincubated with either 10‐5m‐clorgyline or 10‐5m‐deprenyl for 20 and 30 min at 37°C, no MAO activity was seen in any region of the brain. Thus, at the higher preincubation temperature, lower concentrations of each inhibitor and a shorter preincubation period were required for inhibition of the enzyme. Preincubation for 60 min at 37°C with a combination of 10‐7m‐clorgyline and 10‐8m‐deprenyl did not inhibit the enzyme in the circumventricular region completely, but at the same temperature, concentrations of 10‐7m of both inhibitors inhibited the enzyme completely in 10min, Thus the effects of the inhibitors are synergistic. These results indicate that the inhibitory effects of the two inhibitors on the enzyme in circumventricular structures of the brain is time‐ and temperature‐dependent. Moreover, the activity seems to be sensitive to deprenyl even when 5‐HT is used as substrate. The results do not support the idea of the existence of type C MAO, distinct from type A and type B MAO.

Effects of clorgyline and pargyline on deaminated metabolites of norepinephrine, dopamine and serotonin in human cerebrospinal fluid.

Effects of clorgyline and pargyline on deaminated metabolites of norepinephrine, dopamine and serotonin in human cerebrospinal fluid.

Possible heterogeneity of type B monoamine oxidase in pig heart mitochondria

The metabolism in vitro of 5-hydroxytryptamine (5-HT), tyramine and benzylamine by pig heart mitochondrial monoamine oxidase (MAO) has been studied. Linear Lineweaver-Burk plots yielded estimated K m values (at pH 7.8) of 475 μM (5-HT) and 292 μM (tyramine). In contrast, linear regions of a downward-curving reciprocal plot revealed the presence of a high- and low-affinity metabolizing site (estimated K m of 39 and 853 μm respectively) for benzylamine. Studies with the irreversible MAO inhibitor clorgyline indicated that metabolism of the three substrates in this tissue was brought about by type B MAO alone. However, the apparent sensitivity toward clorgyline of each substrate-metabolizing activity was not identical. This was due to different degrees of rapid or possibly instantaneous inhibition of enzyme activity toward each substrate. This rapid inhibition appeared to be both partially reversible and irreversible to a relative degree depending upon the substrate-metabolizing activity studied; additional time-dependent inhibition developing with prolonged preincubation was a first-order process, with a similar half-life, whichever substrate was used to assay MAO activity. Ackermann-Potter and Lineweaver-Burk plots also demonstrated differences in the inhibitory effects of clorgyline upon metabolism of each substrate. The ability of 5-HT, tyramine and benzylamine to inhibit each other's deamination in vitro was also investigated. Enzyme activity was measured by radiochemical assay with each labeled substrate in the presence and absence of the other non-labeled amines. Lineweaver-Burk analysis revealed a competitive interaction between tyramine and benzylamine, whereas mixed-type inhibition patterns were obtained for mixtures containing 5-HT/tyramine or 5-HT/benzylamine. In this latter case, the present inhibition data could only be assessed accurately with the low-affinity catalytic site for benzylamine. The kinetics of heat denaturation indicated both a thermolabile and thermostable component of each substrate-metabolizing activity. Some substrate-dependent differences in the relative proportions of these components were found. These experiments are discussed in relation to similar studies by other workers and suggest that pig heart MAO may, in fact, be heterogeneous.